This invention relates generally to well pumps and more particularly concerns a filter for subsurface oil or water wells which use plunger type pumping apparatus generally lowered through a production tubing string by use of sucker rods. The filter allows sand and other abrasive solids to be filtered out of the fluids produced by such wells.
Sand and other abrasive solids mixed in with the sought after well fluids are a constant cause of inefficiency and failure in oil and water well pumping sytems. They cause damage to the pump and its ball and seat mechanism and to the production tubing pipe string. The likelihood of their presence is increased when a well has been stimulated by sand fracturing or acidizing, which are common practice in the industry.
Many types of filters have been designed for use with oil or water well pumps, but no workable, economical filter is presently known. As a result, such pumps are generally operated without any filter and therefore experience inordinate and costly down time, labor and materials in effectuating repairs.
Most of these filters employ some type of filter media packed between layers of screen or perforated or slotted tubes. The filter media most commonly used are gravel, sand, man-made beads or fiberglass matting. The screens or tubes are generally made of steel, brass or PVC plastic, although other types of material have been tried based on the type of fluid to be filtered. While these filters do produce some filtering action they are neither practical nor cost efficient for modern pumping wells. Their problems are compounded in that they are generally designed to be lowered into the well bore either attached to the production tubing pipe or set or anchored directly to the casting. Installation service or replacement of such filters requires the removal not only of the sucker rods and pump but also either the production tubing or the casing liner. Moreover, because these filters are attached to the bottom of the production tubing string or directly into the casing, they tend to be inadvertently left in the well if the production tubing pipe becomes corroded or stuck in the well bore. The removal of these filtes then becomes a very expensive task requiring special fishing tools or drill equipment.
When placed on the bottom of the production string pipe, these filters generally replace the mud anchor commonly used with such pumps. The mud anchor is a length of pipe which is closed on the bottom and perforated near the top and placed under the pump seat. Gas laden fluid enters through the perforations and is forced to travel downwardly to enter a gas anchor which is attached to the pump. As the fluid travels downwardly separation occurs due to the gas bubbles, which are lighter than the fluid, working their way upwardly and out of the very top perforation in the mud anchor. Filters which do away with the mud anchor sacrifice this gas separation process, thereby decreasing the effeciency of the downhole pump which then must not pump fluid but also must compress gas.
It is, of course, an object of the invention to provide a filter which filters sand and other abrasive from pumped fluids. It is also an object of the invention to provide a filter which reduces the possibilty of sand or trash becoming stuck or lodged in the ball and seat valve mechanism of the common downhole pump. Similarly, it is an object of the invention to provide a filter which reduces the possibility of sand or grit from being pumped into the production tubing pipe string and settling around the top of the pump so that the pump becomes stuck or sand locked in the string. A collateral object of this invention is to provide a filter that will trap the solids which are filtered out and allow them to be removed from the well bore, examined and disposed of.
It is also an object of this invention to provide a filter which attaches directly to the bottom of downhole pumps used in conjunction with sucker rods. A related object of the invention is to provide a filter which can be installed, repaired or serviced by the removal of only the sucker rod string and pump, thus eliminating the costly process the production tubing pipe or casing.
Another object of the invention is to provide a filter which eliminates the need for the common gas anchor assembly and serves the functions of both a filter and a pump manifold. Accordingly, it is also an object of the invention to provide a filter usuable in conjunction with a mud anchor attached to the bottom of the production tubing pipe string to provide a gas separation and dispersal effect.
A further object of the invention is to provide a filter which utilizes readily changeable filter media to accommodate different based fluids or well chemicals. A similar object of the invention is to provide a filter which utilizes readily disposable filter media which are inexpensive and simple to change. Likewise, it is an object of the invention to provide a filter in which the filter media are removable and replaceable while the remainder of the filter is cleanable and resuable. And it is an object of this invention to provide a filter which may be constructed of materials selected to function in various well acidizing treatments or chemical injections.
Still another object of the invention to provide a filter for use with either insert type downhole pumps or tubing liner pumps. And it is an object of the invention to provide a filter that will not be inadvertently lost or stuck in the well bore. Finally, it is an object of the invention to provide a filter sized in accordance with its pump so that pump efficiency is not lost due to intake restriction.